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<h2><a name="SECTION0019310000000000000000">
17.3.1 Example</a>
</h2>
<a name="Signal_Example"></a>
<p>
Here is a minimal example program. It uses the <tt class="function">alarm()</tt>
function to limit the time spent waiting to open a file; this is
useful if the file is for a serial device that may not be turned on,
which would normally cause the <tt class="function">os.open()</tt> to hang
indefinitely.  The solution is to set a 5-second alarm before opening
the file; if the operation takes too long, the alarm signal will be
sent, and the handler raises an exception.

<p>
<div class="verbatim"><pre>
import signal, os

def handler(signum, frame):
    print 'Signal handler called with signal', signum
    raise IOError, "Couldn't open device!"

# Set the signal handler and a 5-second alarm
signal.signal(signal.SIGALRM, handler)
signal.alarm(5)

# This open() may hang indefinitely
fd = os.open('/dev/ttyS0', os.O_RDWR)  

signal.alarm(0)          # Disable the alarm
</pre></div>

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<span class="release-info">Release 2.5.1, documentation updated on 18th April, 2007.</span>
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